Test instruments, such as multimeters, voltage meters, oscilloscopes and the like, are used to measure electrical parameters in various electrical devices. FIG. 1 illustrates an exemplary test instrument 100. The test instrument 100 has a test probe 102 that is coupled to an input/output 104 of the test instrument 100. The test probe 102 has a test lead 106 having a first end 108 that is coupled to the input/output 104 of the test instrument 100 and a second end 110 that is coupled to a probe body 112. The probe body 112 includes a tip 114, which is coupled to a test point (not shown) of a device (not shown) to be measured or tested. As will be clear to a person having ordinary skill in the art, a second test probe (not shown), such as a ground connector, may be coupled to input/output 105.
In general, different length test probe tips are used in various test applications. In the past, to accommodate the need for different length probe tips, various test probe assemblies having different probe tip lengths were used with test instruments. For instance, a user may have two sets of test probes, one probe set with long length probe tips and another set with short probe tips. Another method for accommodating for the need of different length probes has been to use probe tips that are removable from the probe holder or body. Thus, rather than replacing the entire probe assembly, only the probe tip needs to be replaced. However, both of these solutions require a user to have to manage two sets of test probes, either the entire test probe assembly or test probe tips. Often test points are located in an obstructed location and having multiple test probes or probe tips can result in problems for the user when switching out the different probes. For instance, the user may have difficulty carrying the extra probes or the equipment may put the user in an awkward position so that it is a challenge to change out the probes. Additionally, by having separate test probes, the user may misplace, drop, or lose the probes so that the appropriate probe or probe tip is not available when needed.
More recently, however, test probes have been designed with probe tips that are slideable within the probe holder or body. Thus, rather than replacing the entire probe assembly when a different length probe tip is required, the probe tip slides in and out of the probe body and is locked into position at a desired length. For instance, when a longer probe tip is required, a locking mechanism that holds the probe tip within the probe body may be released so that the probe tip is free to move within the probe body. A user may then slide the probe tip so that a greater portion of the probe tip is exposed from the probe body and lock the probe tip into position. Therefore, rather than replacing the probe assembly or the probe tip, a single probe tip may act as a varying length probe tip. When a long probe length is needed, the probe tip slides out of the probe body so that more of the probe tip extends from the probe body. When a short probe length is needed, some of the exposed probe tip slides back into the probe body so that less of the probe tip extends from the probe body. Consequently, a single probe tip provides versatility and a user does not need to carry around probes having varying lengths.
Recently safety standards have been developed that limit the length of the exposed probe tip. In particular, the International Electrotechnical Commission (IEC), under the guidance of Technical Committee (TC66), generated a safety standard for Test and Measurement Equipment related to test probes referenced as IEC-61010-031. This standard specifies requirements for test probe tips for various test applications. For instance, the safety standard specifies the length of the exposed metal tip of the probe used in industrial applications, referred to as category III (CAT III) and category IV (CAT IV) installation, must be less than 4 mm in length. The probe tip for low energy applications, such as used in household applications or category II (CAT II) installations, must be less than 18 mm in length. Having a probe tip with exposed metal 18 mm in length is important because this allows users to easily insert the probe tip into a standard wall socket for quick and accurate measurement, which is not possible with a 4 mm probe tip. For industrial applications (CAT III and CAT IV) where high energy exists, a reduced probe tip of 4 mm is important to help reduce risk of arcs and arc flash hazards, which is not an issue in CAT II environments.
Therefore, when using a slideable probe tip described above, a user will not know whether the exposed length of the probe tip is within the specified length to meet the safety standard unless a measurement is made on the exposed length of the probe tip each time the probe tip length is adjusted. This requires a user to carry a measurement tool and results in a time consuming second step. Although a user may expose a portion of the probe tip that is significantly less than required by the safety standards discussed above and not have to make a measurement, most applications require the entire amount allowed under the safety standard. For instance, in household application, a user will need a probe tip to be very close to the 18 mm maximum length because it will allow the user to insert the probe tip into standard wall sockets.
There is, therefore, a need for a test probe having an adjustable length probe tip that indexes to predetermined lengths. Additionally, there is a need for an adjustable probe tip that communicates to a user the length of the exposed probe tip.